Adelphi Research Test Deca 400mg

Adelphi Research Test Deca 400mg combines Testosterone and Nandrolone Decanoate in a single vial, delivering the most popular mass-building stack in one convenient injection. This blend provides the anabolic foundation of testosterone alongside Nandrolone’s superior nitrogen retention, collagen synthesis, and joint-protective properties. Instead of drawing from two separate vials and calculating individual doses, this pre-mixed formulation simplifies cycle management for intermediate and advanced users.

Why the Test/Deca Stack Works

The Testosterone and Deca-Durabolin (Nandrolone Decanoate) stack has been the cornerstone of bodybuilding mass cycles since the 1970s. Testosterone provides the androgenic base that maintains libido, mood, and essential male physiological functions during a cycle. Nandrolone adds a unique anabolic effect: it produces steady, quality muscle gains with significantly less water retention than high-dose testosterone alone, while simultaneously increasing collagen synthesis by up to 250% according to research published in the Journal of Clinical Endocrinology and Metabolism (1999).

This collagen synthesis boost is what gives Nandrolone its famous joint-protective effects. Users running heavy compound lifts frequently report reduced joint pain and improved connective tissue resilience during Deca cycles, allowing higher training intensity and volume without the joint wear that typically accompanies heavy lifting on testosterone alone.

Suggested Protocol

• Dose: 1ml (400mg combined) twice per week for a total of 800mg/week, or 1ml once per week for 400mg/week (moderate dose)
• Cycle length: 12-16 weeks (Nandrolone Decanoate has a very long ester and requires extended cycles to reach full effect)
• Aromatase inhibitor: Arimidex 0.25-0.5mg every other day to manage oestrogen from the testosterone component
• Prolactin control: Cabergoline 0.25mg twice per week. Nandrolone is a 19-nor compound that raises prolactin
• PCT start: 21 days after last injection (Deca’s decanoate ester has a 15-day half-life and takes 3 weeks to clear)
• PCT: Nolvadex 40/40/20/20mg for 4-6 weeks. Consider HCG pre-loading during the last 3 weeks of the cycle

What to Expect

• Week 1-4: minimal visible changes. Both compounds are long-ester and require time to reach steady state
• Week 5-8: noticeable fullness, weight gain accelerates, strength climbing on all major lifts. Joints feel healthier under heavy loads
• Week 9-16: peak gains. Quality mass accumulation with manageable water retention (less bloat than high-dose Test alone). Expect 6-10 kg of weight gain over the full cycle

Key Facts

• Active ingredients: Testosterone + Nandrolone Decanoate, 400mg/ml combined
• Manufacturer: Adelphi Research
• Aromatisation: moderate (testosterone component)
• Progestogenic activity: yes (nandrolone raises prolactin)
• Liver toxicity: none (injectable)
• PCT timing: 21 days after last injection (critical: longer wait than standard Test cycles)

Read our Beginner’s Guide if this is your first or second cycle (Test/Deca is not recommended before your third cycle). For PCT protocols specific to Deca, see our PCT Guide. Browse all injectable steroids.