There are some general guidelines but it should be noted that finding a couple of these physical signs are not necessarily indicative of drug abuse. It is a general list of symptoms which may be present with a variety of drugs. Sudden weight loss or gain (usually loss) is very common with some of the more popular drugs today. When combined with an overall change in mood/attitude/behavior, it is even more probable that there may be drug abuse. Needle marks in the arms, legs and the bottom of the feet is a pretty good indication of drug use. Most people who inject drugs will wear long sleeves even in the summer to cover the needle marks.

A big change from the person’s normal behavior may be a cause of worry.
Hyperactivity, silliness, talkativeness and giddiness are common with many abused drugs. If this is a big change from the person’s normal behavior, there may be cause for worry. With alcohol, there is often the smell of alcohol on the person or clothing. Also, with alcohol there may be vomiting and in the more severe cases, incontinence. A sudden need for privacy and keeping doors locked is a warning sign as well, especially if the person acts suspicious or paranoid. Increased trouble with the police is another indication that there is drug use going on. The law may become involved because of increased traffic accidents, violence or other such matters.
An increased and unexplained use and need of money could mean that they are using money to supply their habit. This is a common clue for many loved ones of addicts. A change in friends or places to hang out often occurs in people who have become addicted to drugs or alcohol. Usually the friends and places are not approved of my other family members.
Drugs can often lead the addict to violent or destructive behaviors. Becoming increasingly reclusive can be another indication of addiction. They begin to hide away in their room more often or other places of solitude. Speaking of rooms, an addict will very often have a drug kit right next to their bed so that they can get a fix right when they wake up. This may be one of the reasons they start locking their door against family and friends.