§ Mr. Cohen
To ask the Secretary of State for Health what advice the Chief Medical Officer of Health has provided regarding the time traces of(a) cannabis, (b) marijuana, (c) Ecstasy, (d) cocaine, (e) heroin, (f) tobacco and (g) alcohol remain in the body and cause impairment; and what the estimate of the degree of impairment in each case is of a comparable input after 24 hours. 
§ Ms Stuart
[holding answer 22 January 2001]: The Department's publication "Drug Misuse and Dependence—Guidelines on Clinical Management" contains information on the approximate duration of detectability of a range of substances in urine, which gives an indication of how rapidly substances are metabolised. Information on the risks and effects of substances, including alcohol and tobacco, is included in several publications produced on behalf of the Department, such as "The Score: Facts About Drugs."
It is not possible to determine with any degree of accuracy a comparable dose of the substances named in order to estimate degree of impairment. But, in general, nervous system depressant-type substances (such as heroin) will tend to impair motor functions and the ability to carry out tasks. Hallucinogenic and stimulant-type substances have problematic effects of their own, which may or may not cause impairment in the short-term.
Impairment in an individual will vary according to a range of factors including metabolism, dose, route of administration, regularity of use, and whether taken in combination with other substances.
Copies of "Drug Misuse and Dependence—Guidelines on Clinical Management" are available in the Library. "The Score: Facts About Drugs" is available from the National Drugs Helpline 0800 776600.45W