Abiraterone
Severe
Database
Drug interaction classified as: metabolism
Source: DDInter
Drug reference
Tamoxifen
Selective oestrogen receptor modulator (SERM, triphenylethylene) · Antineoplastic
Also known as Tamoxifen citrate, Nolvadex, Tamofen
START
20 mg PO once daily (ER+ breast cancer); duration 5–10 years
TYPICAL MAX
40 mg/day
STOP IF
VTE, abnormal uterine bleeding/endometrial malignancy, significant hepatotoxicity
WATCH
Annual gynae review/report abnormal bleeding, VTE symptoms, lipids, eye review; avoid strong CYP2D6 inhibitors
CDSCO approvedSchedule H (Prescription Drug in India).ATC L02BA01
KDIGO 2024 + manufacturer label
- ONSET
- 1.3h · absorption onset
- PEAK
- 5h · Cmax
- t½
- 6d · parent t½ (~6 days)
- DURATION
- 1d · once-daily dosing
EXCRETION
Hepatic CYP3A4/2D6; mainly biliary/faecal
route + CYP
INTERACTIONS
12 major
SEVERE in our sources
PREGNANCY
Contraindicated — fetal harm; effective non-hormonal contraception during and ~2 months after
FDA category + note
Top interactionssee all 12 →
- AbirateroneSevereDatabaseDDInter
- AmiodaroneSevereDatabaseDDInter
- AmisulprideSevereDatabaseDDInter
- AnagrelideSevereDatabaseDDInter
Available in India
43 branded formulations. Look up specific brands in the Drugs workspace.
Mechanism
Competitive ER modulation — anti-oestrogenic in breast tissue (blocks oestrogen-driven proliferation) but partial agonist in bone and endometrium; prodrug activated by CYP2D6 to potent metabolite endoxifen.
Indications
Adjuvant and metastatic ER-positive breast cancer (pre- and postmenopausal)Ductal carcinoma in situ; risk reduction in high-risk womenAnovulatory infertility (off-label)
Dosing
- Adult
- 20 mg PO once daily (range 20–40 mg/day; doses >20 mg divided). Typical adjuvant duration 5–10 years.
- Pediatric
- Not routinely (McCune-Albright off-label specialist).
- Renal adjustment
- No specific adjustment.
- Hepatic adjustment
- Caution in hepatic impairment (extensive hepatic metabolism); no fixed adjustment.
- Geriatric
- No specific adjustment.
- Max dose
- 40 mg/day
Pharmacokinetics
Onset
Antitumour effect over weeks–months
Peak effect
Cmax ~5 h; steady state weeks
Duration
Long (accumulates; very long metabolite t½)
Half-life
Parent ~5–7 days; N-desmethyl metabolite ~14 days
Bioavailability
Well absorbed
Protein binding
>99%
Metabolism
Hepatic CYP3A4/CYP2D6 → endoxifen (active)
Excretion
Mainly biliary/faecal; minimal renal
Contraindications
- Concomitant warfarin in DCIS/risk-reduction setting (label)
- History of DVT/PE (risk-reduction setting)
- Pregnancy
- Hypersensitivity to tamoxifen
Side effects
Common
Hot flushesVaginal discharge/bleedingMenstrual irregularityMood changes, fatigueFluid retention
Serious
- Endometrial carcinoma/uterine sarcoma
- Venous thromboembolism (DVT/PE), stroke
- Hepatotoxicity (rare; steatosis)
- Cataracts/retinopathy
- Severe hypertriglyceridaemia/pancreatitis
Pregnancy & lactation
Pregnancy
Contraindicated — fetal harm; effective non-hormonal contraception during and ~2 months after
Lactation
Avoid — may suppress lactation and risk to infant
Drug interactions
Amiodarone
Severe
Database
Drug interaction classified as: synergy.
Source: DDInter
Amisulpride
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Anagrelide
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Anastrozole
Severe
Database
Tamoxifen lowers anastrozole concentration ~27% — antagonistic; do not co-administer
Do not combine; sequence per protocol
Source: Kimi deep-research + Cla
Anisindione
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Arsenic Trioxide
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Bedaquiline
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Bepridil
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Bupropion
Severe
Database
Reduced tamoxifen efficacy (reduced endoxifen).
Consider venlafaxine instead.
Source: DDInter
Cabozantinib
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Carfilzomib
Severe
Database
Drug interaction classified as: synergy
Source: DDInter
Related guidelines
Ask House about Tamoxifen
Continue into a citation-backed clinical answer with the drug context already attached.
Sources: KD Tripathi 7e, Goodman & Gilman 14e, Harrison 22e, Katzung·Verified: 2026-05-19 · House clinical team·Cockpit curated: 2026-05-19