Smoking and mental health - NCSCT

Smoking and mental health
491 NHS stop smoking service (NHS SSS) users also showed that those
succeeding at a quit attempt experienced a marked reduction in anxiety
symptoms compared with baseline, thus contradicting the common assumption
that smoking is a stress reliever. 58
5.4.3 Weight gain
Weight gain can be a significant problem among people with SMI, and reflects
prevalent dietary patterns, low exercise levels and side effects of some
medications. Concerns about additional weight gain resulting from quitting
smoking are relevant in the general population 59 and especially so among
smokers with SMI. 60 In the general population, smoking cessation is typically
associated with a gain in weight of 5 kg or more relative to those who continue to
smoke, and more in those who are already overweight. Similar outcomes might
be expected in people with SMI, although the randomised trial literature on
effects in SMI is not especially informative on this outcome; we are aware of only
one study that has reported change in weight in participants with SMI, which
reported no increase. 35
5.4.4 Interactions with treatment for mental disorders
Metabolism of several psychotropic drugs is increased in cigarette smokers. This
effect is not due to nicotine, but to inhaled polycyclic aromatic hydrocarbons in
smoke, which induce cytochrome P450 (CYP) CYP1A2 isoenzymes 61 to
metabolise many commonly used antipsychotics and antidepressants more
quickly. Patients who smoke are therefore likely to need higher doses of these
drugs to achieve similar blood levels to non-smokers, and in the event of
stopping smoking need to reduce the doses used to compensate for this effect.
This applies in particular to clozapine and olanzapine, two commonly used
antipsychotic medications metabolised primarily by CYP1A2, 62 and
pharmacokinetic studies have demonstrated more rapid clearance of olanzapine
and lower clozapine concentrations in participants who smoke compared with
those who don’t. 63,64 Adverse clinical outcomes arising from rapid increases in
blood levels of these drugs after stopping smoking have been reported, 65,66 with
symptoms including somnolence, hypersalivation, fatigue, extrapyramidal effects,
delirium and seizures. 65,67 Clinical guidelines recommend reducing doses of
these drugs by around 25% during the first week after stopping smoking, and
monitoring blood levels before and at weekly intervals after stopping smoking
until levels have stabilised. 68 Similar considerations apply to a range of other
psychotropic drugs, for which recommendations are given in Table 5.1.
Nicotine is metabolised predominantly by a different CYP enzyme, CYP2A6,
which is induced by oral contraceptive medications and carbamazepine. 61,69
92 © Royal College of Physicians 2013