Switching between testosterone delivery methods isn't as simple as converting milligrams. Each delivery method has different bioavailability, absorption kinetics, and effective dosing ranges. Here's the practical conversion framework and what to expect during the transition.
The Conversion Challenge
Testosterone delivery methods have fundamentally different bioavailability:
| Method | Bioavailability | Meaning |
|---|---|---|
| Injectable (IM/SubQ) | ~100% | Virtually all injected testosterone enters systemic circulation |
| Topical gel (1%) | ~10% | Only ~10% of applied dose is absorbed through skin |
| Topical cream (compounded) | ~10–20% | Higher concentration creams improve absorption somewhat |
| Oral TU (with food) | ~3–7% | Lymphatic absorption is highly variable |
| Nasal (Natesto) | Variable | Rapid but brief peaks; effective average exposure is low |
| Pellets | ~100% | Direct subcutaneous release; fully bioavailable |
Because bioavailability varies by 10–30x across methods, dose "conversion" isn't a simple multiplication. A man on 100mg/week injectable is not equivalent to a man applying 100mg/day of cream — despite the similar-sounding numbers.
Approximate Conversion Table
| From | Weekly Equivalent | To | Approximate Dose |
|---|---|---|---|
| Injectable cypionate 100mg/week | 100mg | → Topical gel 1% (AndroGel) | 50mg/day (5g of 1% gel) |
| Injectable cypionate 100mg/week | 100mg | → Compounded cream 20% | ~100mg/day applied to skin |
| Injectable cypionate 100mg/week | 100mg | → Oral TU (Kyzatrex) | ~200mg twice daily (start dose; titrate by labs) |
| Injectable cypionate 100mg/week | 100mg | → Natesto | 5.5mg per nostril, 3x daily (fixed dose) |
| Injectable cypionate 100mg/week | 100mg | → Pellets | ~600–800mg total (every 4–6 months) |
Important: These are starting approximations, not exact equivalences. Individual absorption varies enormously — especially for topical and oral routes. The correct approach is to start at the approximate conversion dose, check labs at 4–6 weeks, and titrate based on actual testosterone levels and symptom response.
Transition Timing
Injectable to Topical
Start topical application on the day your next injection would have been due. Testosterone cypionate's 8-day half-life means residual levels from the last injection will bridge the gap while topical absorption establishes. Check labs at 4 weeks — earlier than the usual 6-week check — because topical absorption may differ significantly from predicted.
Topical to Injectable
Stop topical and start injectable on the same day. No overlap period needed — the first injection begins building levels immediately. Check labs at 6 weeks at trough (morning before next injection).
Any Route to Oral TU
Start oral TU at the standard starting dose when discontinuing the previous method. Oral TU reaches steady state within 7–10 days. Check levels at 4–6 weeks — timing the blood draw 4–6 hours after the morning dose (to capture the absorptive peak relevant to efficacy assessment).
Transition Best Practices
- Check labs earlier than usual after switching methods (4 weeks instead of 6)
- Expect the unexpected: Individual absorption variation is large, especially for topical and oral routes
- Don't compare milligrams across methods: 100mg injected ≠ 100mg applied topically ≠ 100mg taken orally
- Allow 6–8 weeks for subjective assessment: How you feel on a new delivery method may take longer to stabilize than the testosterone level itself
The Bottom Line
Approximate, Then Verify
Dose conversion between TRT delivery methods is an approximation, not a formula. Start at the estimated equivalent dose, check labs promptly, and titrate based on your actual response. The transition period (4–8 weeks) requires patience and monitoring — your steady-state testosterone level on the new method may be significantly different from predicted.