Side effects of dementia medication

The common pattern

Most side effects of Cholinesterase Inhibitors (Donepezil, Galantamine, Rivastigmine) occur in the first 1 to 2 weeks of starting or increasing the dose, then settle. Most are gastrointestinal. Memantine has fewer side effects.

By system

Gastrointestinal (commonest)

• Nausea: very common in the first 1 to 2 weeks. Taking with food and adequate hydration helps. Usually settles. The Rivastigmine patch substantially reduces this.
• Diarrhoea: common. Hydration and dietary care.
• Vomiting: uncommon. If persistent, contact your prescriber.
• Reduced appetite and weight loss: common. Smaller frequent meals. Monitor weight monthly; arrange dietitian review if persistent.
• Indigestion: less common.

Neurological

• Vivid dreams or insomnia: common with Donepezil. Try taking in the morning instead of bedtime.
• Dizziness: common. Stand up slowly. Review blood pressure medicines.
• Headache: less common.
• Muscle cramps: less common. Hydration and gentle stretching help.
• Restless legs: occasional. Discuss with your prescriber.
• Seizures: rare. Contact prescriber if any seizure-like episode occurs.

Cardiovascular

• Slow heart rate (bradycardia): common, usually mild. Significant slowing or syncope warrants review.
• Fainting (syncope): rare. Contact prescriber the same day.
• Falls: more common in older adults on Cholinesterase Inhibitors. Review medication, vision, footwear, and home environment.

Skin (Rivastigmine patch)

• Local skin reaction: rotate the patch site daily. Most reactions are mild.
• Allergic skin reaction: rare but requires discontinuation.

Other

• Urinary frequency or urgency: occasional.
• Increased salivation: occasional, usually mild.

Memantine side effects

Memantine has a different profile, with fewer side effects than the Cholinesterase Inhibitors:

• Dizziness;
• Headache;
• Constipation;
• Drowsiness;
• Raised blood pressure (rare);
• Hypersensitivity (rare).

What helps

• Take the medicine consistently at the same time, with food where indicated;
• Slow titration: longer between dose increases if early side effects occur;
• Adequate hydration (1.5 to 2 litres per day);
• Smaller, more frequent meals if appetite is reduced;
• Switch formulation (capsule to patch for Rivastigmine, or move Donepezil from bedtime to morning);
• Switch medicine: from one Cholinesterase Inhibitor to another, often with improvement in tolerability.

When to contact your prescriber

Same-day contact for any of the following:

• Severe or persistent vomiting (more than 24 hours);
• Significant weight loss (more than 5 per cent of body weight);
• Fainting or near-fainting;
• Very slow pulse (under 50 beats per minute);
• Seizure or seizure-like episode;
• Severe new chest pain;
• Severe rash or other allergic reaction.

Routine review for ongoing tolerability concerns at the next scheduled appointment, or sooner if persistent.

Stopping medication

If side effects are intolerable despite reasonable adjustment, the medicine can be stopped. Sudden discontinuation can sometimes produce a step-down in cognitive function over the following weeks. A planned, supervised taper is preferred. Discuss with your prescriber.