Guanethidine and Diethylpropion: Interaction Details
AI-assisted, pharmacist-reviewed · Source data updated Aug 8, 2026 · Sources: FDA labeling, DDInter 2.0, cited literature
Diethylpropion
Guanethidine
No brand names on record
How we grade severity & evidence
Severity levels
- Contraindicated: These should generally not be used together.
- Major: Potentially serious — often needs a change or close monitoring.
- Moderate: Can be significant — usually manageable with monitoring.
- Minor: Usually limited clinical impact.
Evidence grades
- Established: Well documented — supported by controlled studies or strong clinical data.
- Probable: Good supporting evidence, though not definitively proven.
- Suspected: Some evidence suggests this interaction, but it is not well established.
- Possible: Limited or conflicting evidence; the interaction may occur.
- Theoretical: Predicted from the drugs' pharmacology; not yet confirmed in people.
Ratings come from the documented interaction literature and are reviewed by a pharmacist. They describe the documented risk of the combination, not what will necessarily happen to you — your dose, timing, and health picture all matter.
What happens
Decreased guanethidine effectiveness
Interaction Deep Dive
Many anorexiants have demonstrated the ability to displace guanethidine from the neuron and thus antagonize neuronal blockade caused by guanethidine. If an anorexiant is required, it may be necessary to switch to a different antihypertensive medication31.
Why it happens (mechanism)
Antagonism
Literature reports
1 report — tap to read
a) Concomitant administration of diethylpropion and guanethidine has been reported to result in no effect on the hypotensive response of guanethidine in obese hypertensive patients 1. These data contrast to previous animal studies demonstrating inhibition of the antihypertensive response of guanethidine 2. However, more studies are required to confirm the findings of 1.
Common questions
Can I take Guanethidine and Diethylpropion together?
Decreased guanethidine effectiveness Always confirm with your pharmacist or prescriber before making any change.
How serious is the Guanethidine and Diethylpropion interaction?
It is rated moderate. Can be significant — usually manageable with monitoring.
How quickly could this interaction happen?
The documented onset is "rapid". Effects can appear quickly, often within about 24 hours of combining the drugs.
How strong is the evidence for this interaction?
The evidence is graded "theoretical". Predicted from the drugs' pharmacology; not yet confirmed in people.
Questions for your pharmacist
- Does my dose of Guanethidine or Diethylpropion need adjusting while I take them together?
- What symptoms should prompt me to call you or my prescriber right away?
- Does the timing of my doses matter for this combination?
- Is there anything you'd monitor while I'm on both?
References (3)
- Seedat YK & Reddy J: Diethylpropion hydrochloride (Tenuate Dospan(R)) in the treatment of obese hypertensive patients. S Afr Med J 1974; 48:569.
- Day MD: Antagonism of guanethidine and bretylium by various agents (letter). Lancet 1962; 2:1282. PubMed
- Ober KF & Wang RI: Drug interactions with guanethidine. Clin Pharmacol Ther 1973; 14:190-195. DOI
Keep reading about Diethylpropion
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