Guanfacine and Constipation

Yes, guanfacine does cause constipation as a documented adverse effect, with constipation listed as a common side effect in the FDA drug label. 1

Evidence for Constipation as a Side Effect

The FDA drug label for guanfacine explicitly lists constipation among its common adverse reactions, with an incidence of up to 15% in clinical trials at higher doses (3mg) 1
Constipation is considered a class effect of centrally acting alpha-2-adrenoreceptor agonists like guanfacine 2
In long-term clinical studies, constipation was reported in 14% of patients during the first year of treatment with guanfacine, decreasing to 4.1% in the second year 3
The incidence of constipation appears to be dose-dependent, with higher rates observed at higher doses 1, 4

Guanfacine is a centrally acting alpha-2-adrenoreceptor agonist, and constipation is a known effect of this drug class 2, 5
Non-dihydropyridine calcium channel blockers (like verapamil) are also associated with constipation, and are specifically noted as potentially inappropriate medications in people ≥75 years with chronic constipation 2
While both clonidine and guanfacine share similar adverse effect profiles due to their shared mechanism of action, guanfacine may have a somewhat different side effect profile due to its higher specificity for alpha-2A receptors 2, 5

In controlled clinical trials, constipation was reported in:
- 0% of placebo patients
- 0-2% of patients on 0.5-1mg doses
- 5% of patients on 2mg dose
- 15% of patients on 3mg dose 1
In a one-year open-label trial, constipation was reported in 14% of patients at any time during the study, but only 3% by the end of the year 1
Constipation was significant enough to cause treatment discontinuation in some patients during clinical trials 1

When prescribing guanfacine, patients should be informed about the potential for constipation as a side effect 1
For patients who develop constipation while on guanfacine:
- Consider dose reduction if clinically appropriate, as constipation appears to be dose-dependent 1, 4
- Management may include increased fluid intake, dietary fiber, and possibly osmotic laxatives if needed 2
- In cases of severe constipation, stimulant laxatives such as bisacodyl or sodium picosulfate may be considered 2
For patients with a history of constipation or at high risk, consider alternative medications if appropriate for their condition 2

Adverse effects of guanfacine, including constipation, tend to decrease over time with continued use 1, 3
Guanfacine should not be abruptly discontinued after prolonged use, as rebound hypertension can occur; the medication should be tapered off 5
The extended-release formulation of guanfacine is FDA-approved for ADHD treatment, while immediate-release formulations are typically used for hypertension 5
Side effects appear to be less severe when doses are maintained below 3mg daily 4