* During the Sydney Olympics a cleaner received a needle stick injury whilst cleaning an Australian athlete's room, but the needle turned out to be for a vitamin shot. This is a real pain in the ass for monitoring cyclists as many top athletes will inject themselves with vitamins in between races to recover faster. The equipment is nearly identical to what you would need to dope your blood or do EPO.
* If somebody is having to either have a massive number of blood draws or injections -- or both -- for medical reasons, they might actually have to carry around a card or other paperwork verifying that the tracks are all perfectly legitimate. In particular, the Red Cross can issue cards to verify why a frequent donor might have suspicious-looking scars.
* Not quite following the trope as straight as others, but pretty close: When somebody is taking medication for mental illness, many people (especially people such as MoralGuardians and TheFundamentalist) tend to think that it's as if they were taking something recreationally. This can lead to embarrassment and awkward situations.
** Doubly so if it's a [[ChurchOfHappyology Scientologist]], as they view the two as one and the same. Since its inception, the Church of Scientology has held that psychiatry is nothing more than a crooked racket of drug-pushers (it was one of Creator/LRonHubbard's big {{Berserk Button}}s, as psychiatrists were instrumental in opposing his Dianetics self-help system), and therefore, people who use medication to treat mental illness are junkies who are kept addicted by their greedy doctors. Creator/TomCruise infamously landed in hot water for this when he criticized Brooke Shields for taking antidepressants.
* Epileptic seizures can come across like drunkenness or drug intoxication to an untrained observer, especially because someone unfamiliar with epilepsy most likely equates "seizure" with grand mals (in which one collapses) and not with a petit mal seizure (which involve a general 'spacing out') or temporal lobe seizures (with mood swings and hallucinations).
** Epileptics take a wide range of drugs and they come in both pill and injected forms.
* Diabetics undergoing insulin shock/hypoglycemia often appear drunk. It's actually a medical emergency. Similarly, ''hyper''glycemia can be mistaken for someone being on amphetamines.
** Similarly, many diabetics don't like checking their blood sugar (which requires a pinprick on the finger or arm) or taking insulin in public because of this trope. Many diabetics choose to do it in the restroom or another more private place to avoid stares and questions.
* Others who can appear drunk are those with a head injury--slurring, staggering, etc.
* Can happen in some contexts with some illnesses: the more severe or stereotypical the symptoms are, the more likely someone is to be Mistaken for Junkie, ''even if their illness is real.'' Common with several pain syndromes and chronic pain disorders and ADHD - the medications needed to treat them are usually addictive and controlled substances, and the more stereotypical or "over the top" the symptoms are (or, alternately, the more subdued) the more likely the diagnosis is to be missed or dismissed.
** It doesn't help that some people actually ''do'' abuse drugs by tricking or suborning doctors into writing medically unjustified prescriptions, thus setting the stage for genuine sufferers to be mistaken for drug-seekers.
* Hyperthyroidism and hypothyroidism are both very bad for this. Someone severely hyperthyroid will sometimes appear for all intents and purposes to be on something like methamphetamine or similar because the symptoms of severe hyperthyroidism can come across as very similar to those of meth addiction. Hypothyroidism, on the other hand, can present similarly to someone drugged up on sleeping pills or opiates with its tiredness, sluggishness, and similar.
* Because testosterone is a steroid, and therefore a controlled substance in many countries, FTM transgender people often have to deal with this - especially if they use injections or gel instead of implants, and are often advised to keep a copy of their prescription and/or a letter from their treating doctor.
** This also led to quite nasty transphobic discrimination against FTM athletes for a long time - seeing as testosterone is, obviously, a banned substance in most organized athletics, and there ''were'' cases of female non-transitioning athletes doping with it, FTM persons (or even women ''mistaken'' for them such as Caster Semenya) were often disqualified from organized athletic competitions or otherwise forced to "prove" their female gender and that their body was naturally producing any excess of testosterone. This situation is slowly beginning to change with some sports accepting transmen who have legitimate proof they are indeed transitioning to male and whose testosterone levels are within the cisgender male range but still lingers on in others.
** The assumption that transgender (whether FTM or MTF) people are "on drugs" or "more likely to use drugs" also leads to discrimination in many other contexts: for example, some people will refuse to room with/rent property to/work with transmen or transwomen because of this assumption. In some places and some settings, laws have been written to make this discrimination illegal, but in many other places there isn't a law against discriminating against a transgender person, and even if there is a law, ''especially'' if the bigot can play it off to "I think they're on drugs," rather than outright trans hate, it's incredibly hard to do anything about it legally, because discriminating against ''drug users'' is codified into the law itself and heralded as a good way to reduce drug use.
* Patients who have a medically managed addiction, even though the addiction is a side effect of treatment and not being a "junkie," due to being the FunctionalAddict and having a steady, managed supply, are often written off as junkies because they are addicted - never mind that addiction is a medical process as much as it is a mental one, and someone can be ''physically'' dependent on, say, pain medication to treat chronic pain while not using it for recreation.
* In a non-drug variant, anytime a musician appears with powder on their clothes, they will almost automatically be assumed to be using drugs - even if they had just eaten something with powdered sugar on it or it's face powder from freshening stage makeup.
* A certain brand of catnip mouse decided to package the catnip separately and give you a little extra to restuff the mouse with, in a clear plastic tube with a black twist top at the end. People then come into your house to find a crushed, dried green plant in a suspicious-looking tube on your counter. Hilarity ensues.
* Certain groups of people are automatically assumed to be junkies by the majority of others, regardless of evidence or lack thereof. Prostitutes are assumed to be doing their work for the drugs, and the homeless are often assumed to take drugs since they probably up to no good anyways, at least as far as "upstanding" citizens are concerned. While these groups certainly do have members that take drugs, many do not, and the stereotyping just further isolates them from success and acceptance in society.
* Poppy-seed muffins and cakes ''do'' contain trace amounts of opium; not enough to affect the human body, but just barely enough to make a person test positive on a drug test. At least the cheap, off-the-shelf drug tests; more advanced ones are able to tell the difference. Either way, one should be advised not to eat poppy seeds on the day of the drug test, just in case. Confirmed by the Series/MythBusters.
* [[https://en.wikipedia.org/wiki/Auto-brewery_syndrome Auto brewery syndrome]], where bacteria in the gut ferment carbohydrates and turn it into - you guessed it - ethanol, causing them to get intoxicated even if they haven't had any drinks. Which makes this the closest RealLife has to DrunkOnMilk.