  The strong long-range Coulomb interaction between massless Dirac fermions in
graphene can drive a semimetal-insulator transition. We show that this
transition is strongly suppressed when the Coulomb interaction is screened by
such effects as disorder, thermal fluctuation, doping, and finite volume. It is
completely suppressed once the screening factor $\mu$ is beyond a threshold
$\mu_{c}$ even for infinitely strong coupling. However, such transition is
still possible if there is an additional strong contact four-fermion
interaction. The differences between screened and contact interactions are also
discussed.
