Common symptoms of drug effects:
1. Stimulates (speed, cocaine) - lot of energy, unable to be calm, increased temperature
2. kanabinoids (marijuana, THC) - red eyes, huge appetite, avoiding eye contact, if it`s not skunk or something like that-laughing
3. Depressants (alcohol, GHB) - little dose-euphoria, good mood, bigger one - slow reactions
4.Inhalatns - disorientation, euphoria, slow reaction
5.Opiates(heroin, buprenorphine or Subutex, methadone)- increased temperature
- Euphoria, and day dreaming for heroin, for others-it can be euphoria, communication
6.hallucinogens(LSD, datura, PCP; atropa belladona, bufothenine,...) - disorientation, looking at the air like someone is there
From the personal experience I know that user is usually tired, exhausted, uninterested, not willing to talk about the drugs (he changes the subject), has got difficulty sleeping, or he throws up often, he`s sweating, he`s shaking... So, disorders in behaviors (even irritability or panic), or/and in physically functioning.
It`s also important… the age of a person (teenager can be moody) or his pychological state (schizophrenia, depression, manic depression).
The most important thing: the person you help must be willing to be helped, you should be calm and reasonable when you asking the person about it, you should not yell or be impulsive, you should be understandable and ready to hear the truth (you may surprise) and offer him help IF HE WANTS your help. Be supportive.
And do NOT use this advice or information to force somebody to do something he does not want.
Hope I helped
Depends on the drug. There are different indicators for different drugs. Can you be more specific. What behavior are you seeing that is making you suspect?