How to use theorem environment in list

Question

I am trying to use theorem environment as a list item. But there are problems with spaces if I use

...
\begin{itemize}
\item
\begin{theorem}
This is a theorem. This is a theorem. This is a theorem. This is a theorem.
\end{theorem}
\end{itemize}
...

It starts the theorem in the next line of the bullet. Even if I use \item[] instead of \item, then the extra space is there between the preceding list item and this one. If I use the \nolinebreak command just after \item, that shows error. If I enclose the theorem inside a \parbox, then with different alignments of the \parbox, we get different alignments of the theorem, taking it to be a single character, but not the desired alignment (note that we get the desired alignment with \parbox for short line, since it makes it a large symbol and then centers it, but it creates problem for large theorem statement).

How do I align the first line of the theorem with the bullet, normally like an item in a list?

The preamble of my original document is

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage{tikz}
%\usetikzlibrary{mindmap}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{arrows,automata,positioning}
\usepackage{amssymb,amsmath,amsthm}
\newtheorem*{theorem}{Theorem}
\newtheorem*{lemma}{Lemma}
\newtheorem*{corollary}{Corollary}
\theoremstyle{definition}
\newtheorem*{definition}{Definition}

\usepackage{float,graphicx}

\usepackage{hyperref}
\hypersetup{colorlinks=true}

A minimal working example is as follows:

\documentclass{article}
\usepackage{amsthm}
\newtheorem*{theorem}{Theorem}
\begin{document}
\begin{itemize}
\item
\begin{theorem}
    This is a theorem.
\end{theorem}
\end{itemize}
\end{document}

Answer 1

Maybe you could define your own theorem environment like this:

\documentclass{article}

% Hand made theorem
\def\claim{\noindent{\bf Theorem.}\itshape\ }
\def\endclaim{\par}
\newenvironment{thm}{\claim}{\endclaim}

\begin{document}
\begin{itemize}
\item\begin{thm} This is a theorem.\end{thm}
\item This is some Text.
\item \begin{thm} And this an other theorem.\end{thm}
\end{itemize}
\end{document}

This is based on a redefinition of the theorem environment.