The UK Food Standards Agency has recommended that pregnant women should limit their caffeine intake, out of prudence, to less than 200 mg of caffeine a day – the equivalent of two cups of instant coffee, or one and a half to two cups of fresh coffee. The American Congress of Obstetricians and Gynecologists (ACOG) concluded in 2010 that caffeine consumption is safe up to 200 mg per day in pregnant women. For women who breastfeed, are pregnant, or may become pregnant, Health Canada recommends a maximum daily caffeine intake of no more than 300 mg, or a little over two 8 oz (237 mL) cups of coffee.

The evidence for or against the importance of limiting caffeine intake during pregnancy is insufficient and of low quality. There are conflicting reports in the scientific literature about caffeine consumption during pregnancy. A 2011 risk analysis review found that caffeine consumption during pregnancy does not appear to increase the risk of congenital malformations, miscarriage or growth retardation even when consumed in moderate to high amounts. There is some evidence that the hormonal changes during pregnancy slow the metabolic clearance of caffeine from the system, causing a given dose to have longer-lasting effects (as long as 15 hours in the third trimester). There is some evidence that higher caffeine intake by pregnant women may be associated with a higher risk of giving birth to a low birth weight baby, and may be associated with a higher risk of pregnancy loss. A systematic review, analyzing the results of observational studies, suggests that women who consume large amounts of caffeine (greater than 300 mg/day) prior to becoming pregnant may have a higher risk of experiencing pregnancy loss.

Health Canada has not developed advice for adolescents because of insufficient data. However, they suggest that daily caffeine intake for this age group be no more than 2.5 mg/kg body weight. This is because the maximum adult caffeine dose may not be appropriate for light weight adolescents or for younger adolescents who are still growing. The daily dose of 2.5 mg/kg body weight would not cause adverse health effects in the majority of adolescent caffeine consumers. This is a conservative suggestion since older and heavier weight adolescents may be able to consume adult doses of caffeine without suffering adverse effects.

The International Agency for Research on Cancer of the World Health Organization has classified alcohol as a Group 1 carcinogen.

Research has shown that moderate levels of alcohol consumed with meals does not have a substantial impact on blood sugar levels. A 2005 study presented to the American Diabetes Association suggest that moderate consumption may lower the risk of developing Type 2 diabetes.

Having a particular genetic variant (A-allele of ADH1B rs1229984) is associated with non-drinking and lower alcohol consumption. This variant is also associated with favorable cardiovascular profile and a reduced risk of coronary heart disease compared to those without the genetic variant, but it is unknown whether this may be caused by differences in alcohol consumption or by additional confounding effects of the genetic variant itself.

Some research has suggested that high levels of fluoride exposure may adversely affect neurodevelopment in children, but the evidence is of insufficient quality to allow any firm conclusions to be drawn.

While little detailed genetic research has been done, it has been shown that alcoholism tends to run in families with possible involvement of differences in alcohol metabolism and the genotype of alcohol-metabolizing enzymes.

Excess fluoride consumption has been studied as a factor in the following:

Strong evidence links pesticide exposure to birth defects, fetal death and altered fetal growth. Agent Orange, a 50:50 mixture of 2,4,5-T and 2,4-D, has been associated with bad health and genetic effects in Malaya and Vietnam. It was also found that offspring that were at some point exposed to pesticides had a low birth weight and had developmental defects.

A number of pesticides including dibromochlorophane and 2,4-D has been associated with impaired fertility in males.

Pesticide exposure resulted in reduced fertility in males, genetic alterations in sperm, a reduced number of sperm, damage to germinal epithelium and altered hormone function.

Chronic excessive alcohol abuse is associated with a wide range of skin disorders including urticaria, porphyria cutanea tarda, flushing, cutaneous stigmata of cirrhosis, psoriasis, pruritus, seborrheic dermatitis and rosacea.

A 2010 study concluded, "Nonlight beer intake is associated with an increased risk of developing psoriasis among women. Other alcoholic beverages did not increase the risk of psoriasis in this study."

Regular consumption of alcohol is associated with an increased risk of gouty arthritis and a decreased risk of rheumatoid arthritis. Two recent studies report that the more alcohol consumed, the lower the risk of developing rheumatoid arthritis. Among those who drank regularly, the one-quarter who drank the most were up to 50% less likely to develop the disease compared to the half who drank the least.

The researchers noted that moderate alcohol consumption also reduces the risk of other inflammatory processes such as cardiovascualar disease. Some of the biological mechanisms by which ethanol reduces the risk of destructive arthritis and prevents the loss of bone mineral density (BMD), which is part of the disease process.

A study concluded, "Alcohol either protects from RA or, subjects with RA curtail their drinking after the manifestation of RA". Another study found, "Postmenopausal women who averaged more than 14 alcoholic drinks per week had a reduced risk of rheumatoid arthritis..."

A number of studies have shown that tobacco use is a significant factor in miscarriages among pregnant smokers, and that it contributes to a number of other threats to the health of the fetus. It slightly increases the risk of neural tube defects.

Environmental tobacco smoke exposure and maternal smoking during pregnancy have been shown to cause lower infant birth weights.

Studies have shown an association between prenatal exposure to environmental tobacco smoke and conduct disorder in children. As well, post-natal tobacco smoke exposure may cause similar behavioral problems in children.

Women who smoke have about a 50% higher chance of giving birth to a child with behavioral disorders, such as ADHD, but a recent study in a book called "Attention Deficit Disorder: A Different Perception" overturns this, saying that ADHD is a genetic trait. Proof of this comes from a study showing that the people with ADHD had higher levels of certain hormones, as Thom Hartman explains with the hunter vs. farmer hypothesis.

Hangovers occur commonly.

- A study in college students found that 25% had experienced a hangover in the previous week and 29% reported losing school time for hangover recovery.

- 15% of men and women who have consumed alcohol experience hangovers at least monthly and ten percent of British men reported hangover-related problems at work at least monthly.

- An estimated 9.23% (11.6 million workers) of the U.S. labor force work with a hangover.

- About 23% of drinkers do not report any hangover after drinking to intoxication.

Smoking is known to increase levels of liver enzymes that break down drugs and toxins. That means that drugs cleared by these enzymes are cleared more quickly in smokers, which may result in the drugs not working. Specifically, levels of CYP1A2 and CYP2A6 are induced: substrates for 1A2 include caffeine and tricyclic antidepressants such as amitriptyline; substrates for 2A6 include the anticonvulsant, valproic acid.

Complications of benzodiazepine abuse include drug-related deaths due to overdose especially in combination with other depressant drugs such as opioids. Other complications include: blackouts and memory loss, paranoia, violence and criminal behaviour, risk-taking sexual behaviour, foetal and neonatal risks if taken in pregnancy, dependence, withdrawal seizures and psychosis. Injection of the drug carries risk of: thrombophlebitis, deep vein thrombosis, deep and superficial abscesses, pulmonary microembolism, rhabdomyolysis, tissue necrosis, gangrene requiring amputation, hepatitis B and C, as well as blood borne infections such as HIV infection (caused by sharing injecting equipment). Long-term use of benzodiazepines can worsen pre-existing depression and anxiety and may potentially also cause dementia with impairments in recent and remote memory functions.

Use is widespread among amphetamine users, with those that use amphetamines and benzodiazepines having greater levels of mental health problems and social deterioration. Benzodiazepine injectors are almost four times more likely to inject using a shared needle than non-benzodiazepine-using injectors. It has been concluded in various studies that benzodiazepine use causes greater levels of risk and psycho-social dysfunction among drug misusers.

Poly-drug users who also use benzodiazepines appear to engage in more frequent high-risk behaviors. Those who use stimulant and depressant drugs are more likely to report adverse reactions from stimulant use, more likely to be injecting stimulants and more likely to have been treated for a drug problem than those using stimulant but not depressant drugs.

Conditions of fatigue correlate positively with increased alcohol consumption.

Although the incidence of underage drinking is still significant, government, university and national statistics have confirmed that alcohol use and binge drinking among high school students has declined steadily over the past three decades, and continues to decline annually. According to a United States Substance Abuse and Mental Health Services Administration study involving 30,000 youths aged 12 to 20 years old, between 2002 and 2013 the percentage of underage drinkers declined from 28.8% to 22.7%. Underage binge drinkers decreased 19.3% to 14.2%. A December 2014 study performed by the University of Michigan also found that 75% of senior high school students disapproved of drinking excessively on the weekends. Alcohol still proved to be the favored substance of abuse among American youths however, with tobacco and illicit drugs following in rank.

An alcohol enema is a faster method of alcohol intoxication since the alcohol is absorbed directly into the bloodstream. The lower gastrointestinal tract lacks the alcohol dehydrogenase enzyme present in the stomach and liver that breaks down ethanol into acetylaldehyde, which is actually more toxic than ethanol (drinking alcohol) and is responsible for most chronic effects of ethanol. When rectally absorbed, ethanol will still eventually arrive at the liver, but the high alcohol content could overwhelm the organ. Additionally, consuming the alcohol rectally neutralizes the body's ability to reject the toxin by vomiting.

Individuals with a substance abuse history are at an increased risk of misusing benzodiazepines.

Several (primary research) studies, even into the last decade, claimed, that individuals with a history of familial abuse of alcohol or who are siblings or children of alcoholics appeared to respond differently to benzodiazepines than so called "genetically healthy" persons, with males experiencing increased euphoric effects and females having exaggerated responses to the adverse effects of benzodiazepines.

Whilst all benzodiazepines have abuse potential, certain characteristics increase the potential of particular benzodiazepines for abuse. These characteristics are chiefly practical ones—most especially, availability (often based on popular perception of 'dangerous' versus 'non-dangerous' drugs) through prescribing physicians or illicit distributors. Pharmacological and pharmacokinetic factors are also crucial in determining abuse potentials. A short elimination half-life, high potency and a rapid onset of action are characteristics which increase the abuse potential of benzodiazepines. The following table provides the elimination half-life, relevant potency to other benzodiazepines, speed of onset of action and duration of behavioural effects.

Moderate alcohol consumption 30–60 minutes before sleep, although decreasing, disrupts sleep architecture. Rebound effects occur once the alcohol has been largely metabolized, causing late night disruptions in sleep maintenance. Under conditions of moderate alcohol consumption where blood alcohol levels average 0.06–0.08 percent and decrease 0.01–0.02 percent per hour, an alcohol clearance rate of 4–5 hours would coincide with disruptions in sleep maintenance in the second half of an 8-hour sleep episode. In terms of sleep architecture, moderate doses of alcohol facilitate "rebounds" in rapid eye movement (REM) following suppression in REM and stage 1 sleep in the first half of an 8-hour sleep episode, REM and stage 1 sleep increase well beyond baseline in the second half. Moderate doses of alcohol also very quickly increase slow wave sleep (SWS) in the first half of an 8-hour sleep episode. Enhancements in REM sleep and SWS following moderate alcohol consumption are mediated by reductions in glutamatergic activity by adenosine in the central nervous system. In addition, tolerance to changes in sleep maintenance and sleep architecture develops within 3 days of alcohol consumption before bedtime.

OP pesticide exposure occurs through inhalation, ingestion and dermal contact. Because OP pesticides disintegrate quickly in air and light, they have been considered relatively safe to consumers. However, OP residues linger on fruits and vegetables. Certain OP pesticides have been banned for use on some crops, for example methyl parathion is banned from use on some crops while permitted on others.

The Environmental Working Group has developed lists for concerned consumers, identifying crops with the highest pesticide residue quantities and the lowest. The "Dirty Dozen" crops are updated yearly and in 2012 included apples, celery, sweet bell peppers, peaches, strawberries, imported nectarines, grapes, spinach, lettuce, cucumbers, domestic blueberries and potatoes. Forty-five fruits and vegetables are listed by the Environmental Working Group as being regularly found with pesticide residue associated with OPs.

Several factors which do not in themselves cause alcohol hangover are known to influence its severity. These factors include personality, genetics, health status, age, sex, associated activities during drinking such as smoking, the use of other drugs, physical activity such as dancing, as well as sleep quality and duration.

- Genetics: alleles associated with aldehyde dehydrogenase (ALDH) and flushing phenotypes (alcohol flush reaction) in Asians are known genetic factors that influence alcohol tolerance and the development of hangover effects. Existing data shows that drinkers with genotypes known to lead to acetaldehyde accumulation are more susceptible to hangover effects. The fact that about 25% of heavy drinkers claim that they have never had a hangover is also an indication that genetic variation plays a role in individual differences of hangover severity.

- Age: some people experience hangovers as getting worse as one ages. This is thought to be caused by declining supplies of alcohol dehydrogenase, the enzyme involved in metabolizing alcohol. Although it is actually unknown whether hangover symptoms and severity change with age, research shows that drinking patterns change across ages, and heavy drinking episodes that may result in hangover are much less often experienced as age increases.

- Sex: at the same number of drinks, women are more prone to hangover than men, and this is likely explained by sex differences in the pharmacokinetics of alcohol. Women attain a higher blood alcohol concentration (BAC) than men at the same number of drinks. At equivalent BACs, men and women appear to be indistinguishable with respect to most hangover effects.

- Cigarette smoking: acetaldehyde which is absorbed from cigarette smoking during alcohol consumption is regarded as a contributor to alcohol hangover symptoms.

The International Agency for Research on Cancer (IARC), found that organophosphates may possibly increased cancer risk. Tetrachlorvinphos and parathion were classified as "possibly carcinogenic", malathion, and diazinon.

Alcohol intoxication, also known as drunkenness among other names, is a physiological condition that may result in psychological alterations of consciousness. Drunkenness is induced by the ingestion or consumption of alcohol in a living body. Alcohol intoxication is the result of alcohol entering the bloodstream faster than it can be metabolized by the body. Metabolism results in breaking down the ethanol into non-intoxicating byproducts.

Some effects of alcohol intoxication, such as euphoria and lowered social inhibition, are central to alcohol's desirability as a beverage and its history as one of the world's most widespread recreational drugs. Despite this widespread use and alcohol's legality in most countries, many medical sources tend to describe any level of alcohol intoxication as a form of poisoning due to ethanol's damaging effects on the body in large doses. Some religions consider alcohol intoxication to be a sin.

Symptoms of alcohol intoxication include euphoria, flushed skin, and decreased social inhibition at lower doses, with larger doses producing progressively severe impairments of balance, and decision-making ability as well as nausea or vomiting from alcohol's disruptive effect on the semicircular canals of the inner ear and chemical irritation of the gastric mucosa.

Sufficiently extreme levels of blood-borne alcohol may result in coma or death.