Medication and Diet 321Pharmacodynamics
Once a drug has reached the brain, its effect depends on its interactions
with drug receptors. There are major developmental changes in the num-
ber and relative proportion of different types of receptors. Since a single
drug may activate multiple receptor types, and since these various receptor
types may have markedly different effects, developmental changes in
the balance of receptor types can result in the same drug having very
different effects on children and adults. Perhaps this is why stimulants
can produce euphoria in adults but not in children, tending, if anything,
to make children dysphoric. Psychotropic drugs that work in adults do
not necessarily work in children, and vice versa. Furthermore, drugs
familiar to adult psychiatrists for one set of disorders may be used by
child and adolescent psychiatrists for a rather different set of disorders. For
example, tricyclics work well for adult depression but not for childhood or
adolescent depression, yet relatively low doses of tricyclics can be used to
treat childhood enuresis or ADHD.
Medication: specific groups of drugs
Stimulants
Either methylphenidate or dexamfetamine is usually the drug of choice
for the treatment of ADHD (including the subgroup of ADHD that meets
the ICD-10 criteria for ‘hyperkinesis’). They have mixed dopaminergic and
noradrenergic actions. Indications and side effects are discussed in detail in
Chapter 5. They have a powerful effect, usually reducing ADHD by around
one standard deviation. Since most of those treated with stimulants are
two or three standard deviations above the average, stimulants typically
reduce rather than abolish ADHD symptoms – emphasising the need for
educational and behavioural help too. When ADHD is associated with dis-
ruptive behavioural problems, stimulant treatment often improves these
behavioural problems as well as the ADHD symptoms.
The fact that stimulants have a short half-life and duration of action can
be an advantage: doses in the morning and at midday improve attention
for schoolwork and homework, but unwanted suppression of appetite
and sleep wear off by evening, allowing the individual to catch up on
food intake and then get to sleep. Disadvantages of the short half-life
include fluctuating effectiveness during the day and rebound worsening of
symptoms in the late afternoon or early evening. If these are troublesome,
slow-release preparations are available.
ADHD in children with autistic spectrum problems or an intellectual
disability may also be helped by stimulants, but sometimes at the cost of a
worsening in repetitive behaviours (see Chapters 4 and 28).
Given mixed evidence as to whether stimulants usually precipitate or
aggravate tics, some clinicians avoid using stimulants for treating ADHD
when the child or adolescent has a tic disorder or a strong family history
of tic disorders, employing alternatives such as guanfacine or imipramine