Background Most telephone quitlines provide free nicotine replacement therapy (NRT). An 8-week course is recommended, but few users complete it. Information is needed to help quitlines distribute NRT cost-effectively.

Design Randomised two-group trial.

Setting/participants Colorado QuitLine callers who smoked 16–20 cigarettes per day at enrolment and who were eligible for and agreed to receive free NRT.

Intervention Provision of 4-week versus 8-week NRT supply; the 8-week supply was shipped in halves and required participants to request the second half (split-shipment protocol). Enrolment occurred during March 2010–February 2011, follow-up concluded in November 2011, and analysis was performed in 2012.

Main outcome measures Point abstinence (7 and 30 day) and prolonged abstinence (6 month) from tobacco use.

Results Overall, 1495 study participants were enrolled and 57.7% completed follow-up. Abstinence rates did not differ significantly between study conditions: 13.8% versus 12.4% in 4-week versus 8-week arms, respectively, (30-day point abstinence, non-respondents treated as smokers). NRT duration was similar in both groups, due in part to purchase of additional patches in the 4-week group. About one-third of the 8-week group requested the full 8-week supply and had higher abstinence rates. Cost per quit was lower in the 4-week (compared to 8-week) group.

Conclusions A randomised trial did not find worse cessation outcomes among quitline users who received half the minimum recommended course of NRT, but offering the full recommended course using a split-shipment protocol may be reasonably cost-effective and supportive of NRT adherers.

Trial registration number NCT01889771.