Smoking and Interactions with Medication

Antipsychotics
Chlorpromazine Plasma levels may increase May need to decrease dose. Monitor for
increase in adverse effects.
Clozapine Plasma levels may increase by
72%.
Reduce dose gradually over a week until
75% of original dose. Repeat level.
Consider further reductions.
Clozapine +
valproate
Effect of stopping smoking in
patients who take both
clozapine & valproate may be
more marked then those on
clozapine alone.
Valproate inhibits clozapine metabolism
in non-smokers (+16%)
Valproate induces clozapine metabolism
in smokers (-22%)
Smoking induces clozapine metabolism
by 20% if not taking valproate
Smoking induces clozapine metabolism
by 46% if taking valproate
Fluphenazine Plasma levels may increase Reduce dose by 25%. Monitor for 4-8 weeks.
Consider further reductions
Haloperidol Plasma levels may rise by 23% Reduce dose by 10% & monitor. Consider
further reductions.
Olanzapine Increase half-life by 21% Reduce dose by 25%. After 1 week repeat
plasma levels & consider further reductions
Mood Stabilisers
Lithium +
caffeine
Smoking induces CYP1A2 &
caffeine is metabolised by this
enzyme. Theoretically stopping
smoking may increase xanthine
levels, which could increase lithium
excretion thereby reducing plasma
levels.
If taking caffeine, may need to increase
dose. Monitor weekly.
Antidepressants
Duloxetine Plasma levels may increase by
50%
May need to decrease dose
Fluvoxamine Increase plasma levels May need to decrease dose
Anxiolytics & Hypnotics
Benzodiazepines Possible increase in plasma levels
due to reduced clearance
Consider reducing dose by 25% over 1 week
Miscellaneous
Beta-blockers May need a lower dose Review dose
Cimetidine Nicotine increases cimetidine
levels
May need to decrease cimetidine dose or
use alternative H2 antagonist e.g. ranitidine
Flecainide Increased plasma level May need to decrease dose
Insulin May need less insulin when stop
smoking
Review dose of insulin and monitor blood
glucose
Propranolol Increased plasma levels May need to decrease dose
Theophylline /
aminophylline
Increased plasma levels Decrease dose by 25 – 33% within 1 week of
stopping smoking. Monitor patient as further
alterations in dosage may be required