  We study the renormalisation of the non-Hermitian
$\mathcal{P}\mathcal{T}$-symmetric scalar field theory with the interaction
$\phi^2(i\phi)^\varepsilon$ using the Wilsonian approach and without any
expansion in $\varepsilon$. Specifically, we solve the Wetterich equation in
the local potential approximation, both in the ultraviolet regime and with the
loop expansion. We calculate the scale-dependent effective potential and its
infrared limit. The theory is found to be renormalisable at the one-loop level
only for integer values of $\varepsilon$, a result which is not yet established
within the $\varepsilon$-expansion. Particular attention is therefore paid to
the two interesting cases $\varepsilon=1,2$, and the one-loop beta functions
for the coupling associated with the interaction $i\phi^3$ and $-\phi^4$ are
computed. It is found that the $-\phi^4$ theory has asymptotic freedom in
four-dimensional spacetime. Some general properties for the Euclidean partition
function and $n$-point functions are also derived.
