Reintroductions are an increasingly common conservation tool used to reverse the decline of threatened species, yet globally reintroduction success remains low. Release methods have the potential to influence the outcome of a reintroduction. We used a brushtail possum (Trichosurus vulpecula) reintroduction to test the use and effect of supportive release measures, testing delayed, immediate and nest-box release treatments. Intensive monitoring of 48 radio-collared possums showed release treatment had no effect on dispersal distance, weight change, reproduction or survival; however possums were generally reluctant to utilise supplementary food or shelter. Dispersal rates varied by treatment, with immediate release possums settling fastest. Equal proportions of possums from each treatment lost weight and used unsafe shelter sites immediately after release, but eventually gained weight and chose safer shelter. Unsafe behaviour combined with weight loss suggests that supplementary food and shelter would be beneficial, yet the efficacy of both was low, presenting a reintroduction conundrum not considered in previous research. In environments with low predation risk and where sufficient shelter is available, weight loss and risky behaviour may not affect long-term reintroduction success and immediate releases are recommended as the most effective reintroduction technique. In contrast, in environments where post-release predation risk is high, the inability of possums to quickly adapt to suitable new food or shelter resources could lead to high post-release mortality unless release methods can be specifically tailored to overcome poor adaptability. An assessment of a species adaptability to new conditions should be used to inform release methods for future reintroductions.